The invention relates to a device for applying a patterning agent to a web advancing in its lengthwise direction, and particularly for applying a liquid dye to a carpet web.
A device for applying a patterning agent to a carpet is known from German Patent 33 15 770 C2, where the web runs below an application bar, with the pile facing up, and an application slit which is open to the bottom is formed in the bar. Opposite to the application slit, the web is supported by a resilient cushion which rests against the back of the carpet web. The patterning agent is a foam which is fed to the application slit at several locations distributed over the working width of the slit. The foam is fed to the individual locations via separate feed lines from a distributor. Upstream of the distributor, in the flow direction, there are valves through which foam from a first foam mixer is fed to the distributor during certain time periods, while foam from a second foam mixer is fed to it at different time periods.
The principle described in German Patent 33 15 770 C2, can be applied to carpet webs oriented with their pile facing down, traversing over an application slit that opens up to the top for applying a dye bath patterning agent.
If the patterning agent is changed when operating an arrangement according to the principle of German Patent 33 15 770 C2, for example if a transition is made from a first color to another color, an amount of first patterning agent still located in the lines between the switch-over valves and the distributor, between the switch-over valves and the exit slit, in the distributor, in the feed lines, and in the individual channels of the application bar is displaced by the new patterning agent. When this occurs, mixing of the two patterning agents occurs, so that on the web there is no defined border between the two colors, but rather a transition state in which mixed shades occur, resulting in scrap or in goods of lesser quality. The length of web segments with such lower quality can be on the order of a meter or more.
Developments in today's textile finishing technology are in the direction of shorter and shorter yardage, down to as little as several hundred meters length for the web. Scrap lengths of one or more meters are thus a marked loss when expensive carpeting is involved. Efforts are therefore being made to reduce the losses which occur in devices of the type described, when a transition to a different patterning agent occurs.
A further development of the current technology is described in German Patent 29 00 712 A1. That patent describes a web that is guided over a pressure table, and an application bar provided with the application slit that rests directly on the web. An electrically activated valve is provided for each individual feed line, directly in front of the exit slit.
The segment from the closing location of the valve to the outer opening of the outlet zone, i.e. to the contact location of the pattern agent with the web, therefore becomes short. The residual amount of patterning agent remaining in the segment is also small. In case of a change of the patterning agent, only the relatively small amount of patterning agent still remaining between the valve and the web is displaced by the new patterning agent, and only this amount can result in mixing.
The transition length on the web is significantly reduced as a result of this approach. In this patent, the distance to the exit location should be as small as can be implemented in technical terms. At the same time, supplying the patterning agent via a plurality of individual valves distributed over the width of the web results in a significant improvement of the uniformity of the application amount per surface unit, crosswise to the web. This occurs because there are no flow-related pressure drops, for example, towards the edges of the web.
An additional feature of the device described in this patent is that by dividing the flow supply among a plurality of individual valves, each of which has a section of the outlet zone assigned to it, it is possible to change the patterning agent not only on the whole web, such as over the entire width of the web, but also to change over narrower width regions at different times, as determined by the number of valves, so that various complex patterns can be obtained. Here again, the shortened transition from one patterning agent to the next is of great significance, because only in this way can be produced sharply defined rectangular patterns on the web. More specifically, the device includes a separate valve for each individual feed line, and the feed lines lead to the application slit as slanted bores, drilled through the slide shoe of the application bar.